According to noted Israeli weather specialist Prof Daniel Rosenfeld of Hebrew University, seeding a hurricane with microscopic dust could sharply reduce its force.
The findings of his study – which showed that dust dropped into the lower part of Hurricane Katrina would have reduced wind speeds and diverted its course – were presented last month at the European Conference on Severe Storms in Trieste, Italy.
Rosenfeld’s concept, which was developed with several colleagues, builds on empirical research which shows that large dust clouds from Africa tend to hinder the formation deep storm clouds and hinder the formation of hurricanes when tropical systems are crossing the Atlantic.
He showed in computer simulations that sowing tiny moisture-seeking particles into the lower reaches of a hurricane would prevent the formation of rain and reduce temperatures, starving the storm of its source of energy.
The process “creates clouds with a large number of small drops that fall very slowly, floating with air molecules, and are less likely to collide with each other and coalesce into rain drops,” Rosenfeld told AFP.
Rosenfeld first tested his model in a control run in an attempt to recreate the conditions of Katrina, which was successful. When he then factored in the effect of cloud seeding – taking into account the impact of sea spray, which would reduce the desired effect – the radius of hurricane-force winds shrunk by at least 25 percent, with wind speeds reduced throughout the hurricane.
“That would affect mainly the sea surge, which means less rising of the water, which might have made the difference in New Orleans,” Rosenfeld said.
The simulated path of the weakened storm curved north as compared to Katrina, and would have made landfall about 130 miles east of New Orleans.
According to Rosenfeld, it would take five to 10 Lockheed C-130s cargo planes to disperse some 200 tons per hour of particles so small – less than one millionth of a metre across – that they would be emitted in the form of smoke. The planes would be hundreds of miles from the eye of the hurricane.
Trying to extend the practice of cloud seeding – commonly used both to make or impede precipitation – to hurricanes, has been a scientific endeavor since the 1960s, when the US government ran a series of experiments called ‘Stormfury’ that attempted to decrease hurricane force by artificially stimulating convection – the vertical transfer of heat and moisture – outside the wall which encases the eye of the storm. The idea, which was abandoned after four tests, was to expand the size of the eye, typically 10 to 40 miles in diameter, and thus slow the destructive winds that swirl around the eyewall.
“I tried to fix some of the problems that prevented Stormfury from working,” he said, adding that he was inspired ain after observing that smoke from forest fires can prevent warm rain from tropical clouds.
Rosenfeld, who has won many awards for his work, including the Schaefer and Thunderbird awards from the Weather Modification Association and the Verner Suomi Medal of the American Meteorological Society, has been studying this field for many years. In 2000 he used satellite data to show that urban pollution was reducing the size of water droplets inside clouds and proposed that this would reduce precipitation from short-lived clouds in hilly regions.
In a follow-up study carried out with Chinese researchers, Rosenfeld discovered that airborne particulate pollution from China’s factories and vehicles is seriously reducing rainfall in hilly areas of the country, a phenomenon that will have dire consequences for water resources.